[Subforms of transcription factor Oct-1 synthesized in lymphocytes]

Transcription factor Oct-1 is ubiquitous, participating in expression of the cell housekeeping genes as well as in differentiation of lymphocytes and activation of transcription of immunoglobulin genes in B cells. A new tissue-specific form of Oct-1 (Oct-1L) was found in lymphoid cells of bone marrow, lymph nodes, spleen, thymus, as well as in the cell lines of B and T lymphocytes at different stages of differentiation. This isoform was not found in embryonal and nonlymphoid tissues and cell lines. The complete structure of the oct-1L mRNA was determined, which generally corresponds to the structure of mouse Oct-1b. The difference between oct-1L and isoforms oct-a, b, and c functioning in all cells is replacement of the long first 5'-terminal exon (the 1U exon) encoding 21 amino acid residues with a short one encoding 10 amino acids in the isoforms Oct-1L and Oct-1R. Interestingly, attempts to find mature oct-1 mRNA simultaneously containing the 1L and 1U exons were unsuccessful. The parallel synthesis of "ubiquitous" isoforms Oct-1a, b, and c as well as tissue-specific Oct-1L and Oct-1R in lymphocytes and their precursors may be due either to a high demand of these cells for Oct-1 or to selective participation of different Oct-1 isoforms in regulation of the housekeeping genes and genes involved in the B and T cell differentiation and synthesis of imminoglobulins.